This application pertains to methods of making an optical fiber bundle, and to articles (e.g., an optical fiber amplifier or laser) that comprises such a bundle.
Fiber bundles are used in a wide variety of optical applications including optical fiber amplifiers, couplers, splitters and cladding-pumped fiber lasers. In an exemplary application, a fiber bundle is used to couple light from a multiplicity of diode light sources to the inner cladding of a double clad fiber device. The bundle is made by fusing together individual optical fibers, typically also tapering the bundle to provide increased light intensity.
It is relatively straightforward to simply fuse multiple fibers into a bundle. However, it is generally difficult to make with high yield fiber bundles having high optical throughput. Thus, it would be desirable to have available a method of manufacturing reliably articles that comprise a fused fiber bundle and have high optical throughput. This application discloses such a method, and articles made be the method.
The technology for fusing two fibers together is well known. See, for instance, U.S. Pat. No. 4,439,221. See also Patent Abstracts of Japan, Unexamined Applications, Vol. 97, No. 8; 96JP-0014873, which discloses a process of making a fiber coupler that comprises coating the two bare fibers with a sol obtained by hydrolysis of silica acid ester (frequently referred to as xe2x80x9cTEOSxe2x80x9d), followed by heating of the coated fibers to fuse the fibers.
In a conventional process, two fibers are twisted together to bring them into intimate contact, and they are heated while the ends are being pulled apart. To combine more than two fibers, the same technique is conventionally used. See, for instance, U.S. patent applications Ser. Nos. 08/897,195 and 08/999,429, respectively filed Jul. 21, 1997 and Dec. 29, 1997 by DiGiovanni et al. for xe2x80x9cTapered Fiber Bundles for Coupling Light Into and Out of Cladding-Pumped Fiber Devicesxe2x80x9d, and xe2x80x9cMethod and Apparatus for Producing Fused Fiber Bundlesxe2x80x9d, respectively. U.S. Pat. Nos. 5,500,917 and 5,682,453 disclose an optical assembly that comprises a glass-based bonding compound and a method of making the assembly, respectively.
All patents, patent applications and other references cited herein are incorporated herein by reference.
Glossary and Definitions
By a xe2x80x9cglass precursor materialxe2x80x9d we mean herein a liquid or particle-containing liquid which, upon heating, leaves an inorganic residue that comprises glassy silica as a major component. Such a material may be a colloidal sol in which glassy particles are suspended in a carrier liquid, e.g., fumed silica in an aqueous medium, or may be a silicon-containing compound which can be converted to silica by heating. An example of such a compound is waterglass (sodium silicate), which condenses upon drying and an subsequently be vitrified thermally. An exemplary organic silicon-containing compound is tetramethyl ammonium silicate, which forms a hard residue upon evaporation of its aqueous solvent. This residue reacts upon heating, forming a glass film as the organics burn away.
A xe2x80x9cparticle-freexe2x80x9d glass precursor material is a glass precursor material to which no colloidal particles are intentionally added, and a xe2x80x9cparticle-containingxe2x80x9d glass precursor material is a glass precursor material to which colloidal particle are added, or which forms colloidal particles.
By a xe2x80x9csubstantially planarxe2x80x9d surface of an optical fiber we mean herein a surface that is nominally planar except for (typically unavoidable) minor departure from planarity. Such departures are inherent in, for instance, fibers that have been drawn from a preform of quadratic, rectangular, hexagonal, etc. cross section.
The instant invention is embodied in a method of making an article (e.g., an optical fiber amplifier or laser) that comprises a fused bundle of optical fibers, the method comprising the steps of providing a bundle of optical fibers, and heating said bundle of optical fibers such that said fused bundle of optical fibers results. Significantly, the method also comprises the step of applying, prior to said heating step, a glass precursor material to said bundle of fibers.
In a first embodiment of the invention, the glass precursor material comprises a colloidal sol (i.e., comprises colloidal particles), and in a second embodiment at least two of the optical fibers comprise substantially planar surfaces facing each other, and with the glass precursor material being particle-free glass precursor material.
Exemplary of colloidal particles that can be used in the practice of the invention is fumed silicia, and exemplary of particle-free precursor material is TEOS (partially hydrolized tetraethyl orthosilicate).
The former precursor material typically is used with bundles of fiber that contain (or are likely to contain) undesirably xe2x80x9cgapsxe2x80x9d, exemplarily bundles of fibers of nominally circular cross section, but not excluding bundles of fibers with substantially planar surfaces. A particle-free precursor material is typically used with substantially gap-less bundles that comprise fibers having substantially planar surface regions (e.g., fibers with quadratic, rectangular or hexagonal cross section, or with xe2x80x9cDxe2x80x9d shaped cross section). The particle-free precursor material serves to maintain, prior to fusing them, the fibers in the bundle in place, resulting in improved fused bundles.